Book Image

Ext JS 4 Plugin and Extension Development

By : Abdullah Al Mohammad
Book Image

Ext JS 4 Plugin and Extension Development

By: Abdullah Al Mohammad

Overview of this book

Ext JS is a pure JavaScript application framework for building interactive web applications using techniques such as Ajax, DHTML, and DOM scripting. Ext JS 4 Plugin and Extension Development is a practical, step-by-step tutorial which guides you to learn and develop ExtJS plugins and extensions. There are a lot of examples with explanations and plenty of code provided to make it easier and quicker to pick up. Starting with the fundamentals, this book introduces some of the ExtJS library and community provided plugins and extensions and finishes with several hands-on, real world development examples. You will get a clear concept of ExtJS plugins and extensions and learn how to use them. You will also learn how to develop an ExtJS plugin and extension by going through several examples with code and screenshots. Ext JS 4 Plugin and Extension Development book will provide you with the knowledge to develop ExtJS plugins and extensions using real-life examples.
Table of Contents (16 chapters)
Ext JS 4 Plugin and Extension Development
About the Author
About the Reviewers

Building an Ext JS extension

Let us start developing an Ext JS extension. In this section we will develop an SMS extension that exactly satisfies the same requirements as the earlier-developed SMS plugin.

We already know that an Ext JS extension is a derived class of existing Ext JS class, we are going to extend the Ext JS's textarea field that facilitates for typing multiline text and provides several event handling, rendering and other functionalities.

Here is the following code where we have created the Extension class under the SMS view within the Examples namespace of an Ext JS application:

Ext.define('Examples.view.sms.Extension', {
  extend : 'Ext.form.field.TextArea',
  alias : 'widget.sms',

  config : {

    perMessageLength : 160,
    defaultColor : '#000000',
    warningColor : '#ff0000'


  constructor : function(cfg) {

    Ext.apply(this, cfg);


  afterRender : function() {

      scope : this,
      change : this.handleChange

    var dom = Ext.get(this.bodyEl.dom);

    Ext.DomHelper.append(dom, {
      tag : 'div',
      cls : 'extension-sms'


  handleChange : function(field, newValue) {

    if (newValue.length > this.getPerMessageLength()) {
      field.setFieldStyle('color:' + this.getWarningColor());
    else {
      field.setFieldStyle('color:' + this.getDefaultColor());


  updateMessageInfo : function(length) {

    var tpl = ['Characters: {length}<br/>', 'Messages:{messages}'].join('');
    var text = new Ext.XTemplate(tpl);
    var messages = parseInt(length / this.getPerMessageLength());

    if ((length / this.getPerMessageLength()) - messages > 0) {

      length : length,
      messages : messages


  getInfoPanel : function() {



As seen in the preceding code, the extend keyword is used as a class property to extend the Ext.form.field.TextArea class in order to create the extension class. Within the afterRender event handler, we provide a code so that when the change event fires off the textarea field, we can execute the handleChange function of this class and also create an Html <div> element within this afterRender event handler where we want to show the message information regarding the characters counter and message counter. And from this section, the logic to show the warning, message character counter, and message counter is the same as we used in the SMS plugin.

Now we can easily create an instance of this extension:


Also, we can supply configuration options when we are creating the instance of this class to override the default values:

Ext.create('Examples.view.sms.Extension', {
    perMessageLength : 20,
    defaultColor : '#0000ff',
    warningColor : "#00ff00"

The following is the screenshot where we've used the SMS plugin and extension:

In the above screenshot we have created an Ext JS window and incorporated the SMS extension and SMS plugin. As we have already discussed on the benefit of writing a plugin, we can not only use the SMS plugin with text area field, but we can also use it with text field.